It is now well established that variations in early sensory experience can produce changes in neuronal organization. The functional significance of these neurological alterations, however, remains unclear. The present proposal is directed toward study of early environmental influences on the development of brain morphology and behavior. It is concerned most directly with perceptual capacities, specifically with how visual pattern perception is affected by postnatal visual deprivation and how such environmental influences on behavior are mediated by morphological change, as revealed by the Golgi technique. By systematic variation of age of onset and duration of monocular deprivation it will be possible to determine (1) whether there is a sensitive period in the rat during which visual experience is necessary for development of normal visual function, and (2) whether this period coincides with a similar critical period for the development of normal cortical morphology. In addition, factors involved in recovery of function after environmental deprivation will be studied and correlated with further morphological change.